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Dead zones

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Gulf of Mexico – The dead zone at the mouth of the Mississippi River, largely caused by annual fertilizer and farm chemical runoff from the Mississippi and the Atchafalaya rivers, is said to cover 7,000 square miles or more, or the size of New Jersey, depending on rainfall or floods. This runoff fuels algae blooms, dropping oxygen levels needed to sustain life. It is considered the largest dead zone in the US. (Source: NOAA, Scientific American)Newscom/File

Chesapeake Bay – The bay, which covers parts of New York, Pennsylvania, Delaware, Maryland, Virginia, and West Virginia, is susceptible to large areas of hypoxia due to farm-related runoff -- including that from Amish farmers. The lack of oxygen and resulting algae blooms are said to kill thousands of tons of fish every year. (Source: Chesapeake Bay Foundation, NOAA, EPA)Newscom/File

Lake Erie (Central Basin) – The bottom waters in the central basin historically lose oxygen in late summer, but the “dead zone” is exacerbated by nutrient runoff and exotic/invasive species like quagga mussels, which spew the algae bloom-forming phosphorus as waste. (Source: EPA, NOAA, Cleveland Plain-Dealer)Newscom/File

The Arabian Sea – This dead zone has high levels of hypoxia because of very high chemical productivity, such as conversion of solar energy and carbon dioxide into other forms, and because it is also affected by monsoon seasons that bring nutrients and other runoff materials into the sea. (Source: Science Daily)Newscom/File

Cape Perpetua, Ore. – A hypoxic dead zone of at least 300 miles that seems to exist only in the summer has been forming off the Oregon coast since 2000. Researchers believe that changing coastal winds and marine conditions are causing the hypoxia, and they've reported massive fish and crab deaths within that area in recent years. Source: Science Now, EPA)Newscom/File

Kattegat Strait – The Kattegat Strait is a 137 mile channel between Denmark and Sweden, forming part of the connection between the North and Baltic seas. It has suffered from hypoxia, or a lack of oxygen, due to industrialization and waste-water treatment facilities. This area has been improved by a reduction in emissions from the plants, as well as reestablishment of wetlands and less fertilizer use in agriculture. It is seen as a success story in restoring life to dead zones. (Source: Encyclopedia Britannica, Understanding environmental pollution: a primer – by Marquita Kaya Hill, 2004)Newscom/File

Baltic Sea - Nine countries ring the Baltic Sea coastline, one of the largest brackish (low-salinity) bodies of water in the world. Dependent on inflows and outflows of salt water, it has a unique biodiversity, which has been negatively affected by overfishing, industrial pollution, and runoff from cities. In addition, Russia wants to build a pipeline from Siberia to Europe through the Baltic, bypassing Eastern European countries. (Source: World Wildlife Fund, RIA Novosti)Newscom/File

Cape Rodney, New Zealand, is ranked by the World Wildlife Fund as one of the top 10 hypoxic zones in the world. Hypoxia is when eutrophication, or the presence of decomposing organic material, reaches the level in which oxygen concentrations fall below the level to sustain life. Cape Rodney is also the site of New Zealand’s first marine reserve, established in 1975. Once environmentally decimated, it is now recovering ecologically. (Source: World Wildlife Fund, New Zealand Department of Conservation)Newscom/File

Gulf of Thailand – The Gulf is fed by Thailand’s four principal rivers. The accelerated agriculture and industry along these rivers, combined with expansion in the Bangkok metropolitan area, have contributed to eutrophication, or a high concentration of nutrients, especially phosphates and nitrates. This causes excessive algae blooms in the water. (Source: Greenpeace)Newscom/File

South China Sea – This coastal zone is currently home to 270 million people, which is expected to double over the next 30 years. Population growth leads to urban runoff and sedimentation; moreover, this is a major oil shipping route. Oil spills have caused a great deal of marine life degradation, aggravated by overfishing and the destruction of mangrove trees for development and shrimp farming. (Source: Encyclopedia of the Earth, South China Sea World Wide Web Virtual Library)Newscom/File